Tire reinforcing plies as a general rule are made up of reinforcing threads of a given physical length, coated in a rubber compound, which are parallel to one another and make a given angle to the longitudinal direction of the said ply.
These plies are obtained from plies known as straight-grain plies in which the reinforcing threads are parallel to the longitudinal direction of the straight-grain ply. Using a cutting means, lengths of ply are taken from the straight-grain ply at a given cutting angle, and the said portions of straight-grain ply are butted together via their respective selvedges to form an angled ply or reinforcing ply.
Numerous devices have been developed in industry for creating reinforcing plies that have the geometric features that are as close as possible to the specifications written for the creation of the tires.
The best known cutting devices operate as a general rule in a centralized way, and supply several assembly machines with continuous reinforcing strips. The assembly machines therefore comprise means capable of picking up the lengths of predetermined physical length that make up the said reinforcing plies. Thus, in order to optimize the productivity of these machines, steps are taken to ensure that straight-grain plies of great width are available.
As an alternative, it is also known practice for the reinforcing plies to be created directly upstream of the assembly machine. In this embodiment, the reinforcing ply is built up of tapes cut at an angle, taken from a straight-grain ply that comes in the form of a narrow strip. The tapes are assembled with one another via their selvedges. In practice, the straight-grain strip and the tapes have a width ranging between 10 and 25 mm.
A device of this type makes it possible to create the reinforcing ply at the desired physical length by a careful choice of the number of tapes that have to be juxtaposed.
By way of example, publication U.S. Pat. No. 3,682,222 gives a more specific idea of the device for assembling tapes in question, which device comprises a first means for delivering the narrow straight-grain strip, a cutting means for detaching a length of strip from the straight-grain strip, a reciprocating handling means for conveying the said length of straight-grain strip of given physical length, already cut at an angle to an assembly belt at a given angle, and an assembly means for welding the lengths of strip together via their respective selvedges.
Publication U.S. Pat. No. 4,411,724 also relates to a means of assembling strips taken from a straight-grain ply comprising a means of transfer between a cutting device and an assembly belt in which the strip is firmly held by magnetic means. However, the transfer of the strip from one belt to another contains regions in which the strip is free to determine its own path and not held by the said magnetic means, which means that unwanted movements of the strip with respect to the machine frame of reference can occur.
The invention relates to an improvement to a device for assembling tapes as described hereinabove.
The problem presented by this type of machine relates to how to maintain the geometric features of the strip and of the tape once the latter has been taken from the continuous strip, throughout the phases of transfer, adjusting to length, cutting and assembly. Specifically, because of its narrow width, the tape is subject to deformations and unwanted movements likely to impair the geometric quality of the reinforcing ply. It is therefore important that, at any moment, the strip or the tape should be kept referenced, with respect to the geometric frame of reference of the machine considered as being known and controllable.
Publication EP 958 913 seeks to provide partial solutions to this set of problems and proposes an improvement in which moving alignment walls positioned on each side of the tape act as guides to align the front and rear selvedges of the tape as precisely as possible. The spacing between the walls is substantially equal to the width of the tape.
However, this device fails to prevent the twistings of the strip that are likely to impair the geometry of the selvedges in contact with the said alignment walls.